1-[[[3-[2-(Dimethylamino)ethyl]-1H-indol 5-yl]-methyl]sulfonyl]pyrrolidinone (Almotriptan) has the formula as given below

Almotriptan is a selective 5-HT1B/1D agonist used as a therapy for migraine headache, shows high and specific affinity for 5-HT1B/1D receptors in cranial vessels, but poor affinity for 5-HT1A and 5-HT7 receptors in peripheral arteries and therefore cause less side effects of hypertension by a central nervous system action and other side effects.
U.S. Pat. No. 5,565,447 discloses Almotriptan, its acid addition salts and the process for preparation. The disclosed process involves the decarboxylation of a carboxylic acid (Formula-I), in an inert organic solvent, in the presence of copper derivatives as a catalyst.

The disclosed process involves the column chromatographic purification with silica gel with methylene chloride:ethanol:ammonium hydroxide (60:8:1) as eluent. The U.S. Patent further discloses that the Almotriptan can be converted to acid addition salts with acids in appropriate solvents. Suitable acid addition salts disclosed are those derived from inorganic acids; for example hydrochloric acid and sulphuric acid.
Spanish Pat. No. 2,084,560 discloses the conversion of Almotriptan to its acid addition salts derived from organic, inorganic acids like malate, tartrate, succinate or hydrochloride. The procedure involved for preparation of DL-malate salt is by saltification with DL-malic acid in 96% ethanol.
Research Disclosure (1998) 412 discloses the synthetic pathway for preparation of Almotriptan by a sequence of reactions starting from the 4-substituted anilines (Scheme-1). The process for preparation of Almotriptan was also disclosed in Tetrahedron, 57 (2001) 1041-1048. The disclosed processes results the Almotriptan whose purity is not mentioned.

In the above-mentioned prior art processes Almotriptan malate with pharmaceutically acceptable purity is achieved by the saltification of pure Almotriptan with malic acid.
It is observed that Almotriptan pharmaceutically acceptable salts being prepared by Almotriptan with less purity is not meeting with the pharmaceutically acceptable quality. There is therefore an unfulfilled need to provide industrially feasible process for the preparation of pharmaceutically acceptable salts of Almotriptan from impure Almotriptan without column chromatography purification as described in the prior art.
To overcome the problem inventors have tried to prepare Almotriptan pharmaceutically acceptable salts through Almotriptan acid addition salts from Almotriptan irrespective of its purity.
It is surprisingly found by the inventors that when the impure Almotriptan is reacted with hydroxy benzoic acids such as 2-Hydroxy benzoic; acid (Salicylic acid) and 4-hydroxy benzoic acid, it selectively forms the corresponding acid addition salt, leaving behind the other related substances and impurities which are otherwise difficult to remove by the conventional methods. The hydroxy benzoic acid salts of Almotriptan are further converted to Almotriptan pharmaceutically acceptable salts with acceptable purity.